1. Field
The disclosed embodiments relate to power supplies for electronic devices. More specifically, the disclosed embodiments relate to techniques for increasing the light-load efficiency of voltage regulators in power supplies using nonlinear inductors with cores of different materials.
2. Related Art
A switched-mode power supply in an electronic device generates an output voltage with a voltage regulator that charges and discharges an inductor using a switched input voltage. The output voltage may then be discharged into a capacitor to drive a load connected to the power supply. Because energy is stored in the inductor and/or capacitor, the switched-mode power supply is generally more efficient than a linear power supply that dissipates excess power in the form of heat.
However, switched-mode power supplies have a number of drawbacks, particularly when used in smaller portable electronic devices such as tablet computers, mobile phones, personal digital assistants (PDAs), and/or portable media players. First, switched-mode power supplies typically include relatively large and expensive inductors compared to other components in the power supplies. The inductors may also be subject to a tradeoff between size and efficiency, in which inductors that are larger and/or more expensive are more efficient than smaller inductors. This tradeoff may interfere with the design of a portable electronic device that needs to be both small and power-efficient.
Inductors in switched-mode power supplies for portable electronic devices may be associated with an additional tradeoff between light-load efficiency and transient response. In particular, a portable electronic device is frequently operated in a low-power state (e.g., a sleep mode) that draws power at very light loads. The efficiency of the switched-mode power supply may be increased at such light loads by increasing the inductance of the inductor in the switched-mode power supply. On the other hand, the response of the switched-mode power supply to transient loads (e.g., during use of the portable electronic device) may be improved by reducing the inductance of the inductor and/or increasing the speed of the control loop for the switched-mode power supply, which decreases the efficiency of the switched-mode power supply.
Hence, the use of portable electronic devices may be facilitated by managing the tradeoffs among size, efficiency, and transient response of power supplies for the portable electronic devices.